# grade 10 math?! please help?

1. The surface area of a sphere is: SA =

If the surface area of the sphere is 113.1 cm2calculate the radius.

2.Sebastian ran a mile race at the Portland relays in a time of 4 minutes 20 seconds.He then ran a 1500 metre race in Kamloops, British Columbia in a time of 3 minutes. His average speed was faster in Kamloops than Portland. True or false?

### 5 Answers

- Big DLv 48 years ago
surface area of a sphere = 4*pi*r^2

113.1 = 4*3.14*r^2

r^2 = 9.00

r = 3 cm

he ran in Portland 5280 feet in 260 seconds for an average speed of 20.3 feet per second

then he ran in Kamloops 1500*3.28 feet or 4920 feet in 180 seconds for an average speed of 27.3 ft/s

true

- 8 years ago
1. SA=4 pi r2 ( ie radius squared)

113.1 = 4*3.17 r2

113.1 = 12.57 * r2

r2 = 8.997 (approx$

Now you work out value of t

2. Not 100% sure but I'd say false as the first race is relay and scone isn't so I can't tell if he ran faster or slower in his part of relay

Source(s): Personal knowledge - 8 years ago
1)SA=4(pi)r^2 R=Squareroot(SA/4pi)

R=squareroot(113.1/4pi)=3

2) First you need to put everything into the same units

1m=3.281ft

1500m=4921.26ft

1609.34=1mile=5280ft

Then find average speed of both

4921.26/((4*60)+20)=18.93ft/sec

5280/(3*60)=29.33ft/sec

so the statement is true

- 8 years ago
surface area of sphere is 4 * pi * r^2 :

So 113 = 4 * pi * r^2

113/4 = pi * r2^

113/(4*pi) = r^2

r= sqrt(113/(4*pi))

r = sqrt(9) = 3

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- Anonymous8 years ago
1.radius is 3.000796073 or 3

2.true